The law here in Illinois says that as a cyclist I “must obey the same traffic laws, signs and signals that apply to motorists.” Even though I’m breaking the law, I frequently use the Idaho Stop; I roll through stop signs and often proceed through red lights after stopping. yet, I’m not a risk taker. Most cyclists aren't. Every time I get on my bike, I intend to return home safely. I’m not generally a scofflaw.
So, why do I (as a cyclist) frequently execute Idaho stops, given that they are not legal in Illinois? It’s really pretty simple. Every time I encounter a car, we have a bike/car interaction. (Bike/bike and bike/pedestrian interactions are also common, but are generally much less risky than those which involve cars.) The more I've considered this, the more it’s become apparent to me that every interaction between two parties (driver, cyclist, pedestrian) implies that a negotiation takes place.
A failed negotiation is a problem. The law attempts to very broadly short-circuit the need for negotiations, but does so in an imperfect fashion. Consider a four-way stop. I arrive at the intersection on my bike and want to continue straight. A car arrives after me from the right and wants to turn right. The law says I have the right-of-way, since I arrived at the intersection first. We have an interaction, and thus, a negotiation.
Strictly interpreted, the law specifies the outcome of that negotiation. I go, then the car goes. However, if we follow the law in the strict sense, and I proceed through the intersection, all I do is open myself up for another interaction and negotiation after both I and the driver have left the intersection, because the car is going to pass me, probably within the next block. That interaction is also governed by law here in Illinois (the three-foot rule). That rule is new (so isn't widely practiced yet), and it’s squishier than, say, the right-of-way rule at the intersection. Judging a three foot distance is more difficult than telling if a car has come to a complete stop. To complicate matters further, as the cyclist being overtaken, I’m at a distinct disadvantage in the negotiation. The driver holds most of the cards. I can move over and take the lane, but since I can’t see the driver, I can’t really tell what effect that maneuver has on him. Is he still going to try and pass me? Have I simply pissed him off? Have I confused him? If I don’t take the lane, am I opening myself up to getting doored? So, let’s back up to the original interaction at the intersection. Instead of using the default negotiation (the “contract” specified by the law?) It seems clear to me that I should yield my right-of-way to the driver to avoid the potentially more problematic future interaction.
Now, let’s consider another situation. I arrive at a stop light with a “no right on red” sign (quite common here in the Chicago area), and a car arrives after me, wanting to turn right. Furthermore, let’s assume nobody is coming from either direction on the cross street (a wasted green light). Should I wait for the light to change? In my mind, no. Just as in the first example, by proceeding through the red light, I avoid the possibility of a future interaction (me going straight, the driver turning) in which I am at a negotiating disadvantage. The driver might not have seen me, or might assume she can complete the turn before I get in her way.
To conclude, I try to ride in a way I feel minimizes interactions (especially with cars), and thus reduces the need to enter into negotiations. Reducing the number of negotiations reduces the chance of a negative result.